1. Field of the Invention
The invention relates to rotary heat exchanger wheel including a means for adjusting the dimensions of a gap face sealing arrangement provided adjacent the wheel while the wheel is hot.
2. State of the Prior Art
Furnaces and incinerators used in many industrial operations generate a relatively high amount of combustible fumes which must be eliminated from the exhaust gases, for example. In the past, the fumes have been burned in order to rid the furnace or incinerator of the combustible gases. A more efficient use of the fuel burned within the furnace would be to use the hot exhaust gases from the furnace to preheat the combustion air for the furnace.
It is known to use a rotary heat exchanger to recover the heat from the hot exhaust gases of a furnace or incinerator. In U.S. Pat. No. 4,022,571 issued May 10, 1977, to Gentry et al, such a furnace structure, including a heat exchanger for exchanging hot exhaust gases with combustion air is disclosed.
The heat exchanger which is disclosed and claimed in the above patent is formed from a ceramic material which has a relatively low coefficient of expansion. An example of such a ceramic material is Cer-Vit material which is manufactured and sold by Owens-Illinois of Toledo, Ohio. The heat exchanger is a rotating ceramic wheel which has a plurality of axially extending passages through which the combustible gas mixture passes on one side of the axis of rotation and the incinerator gases pass on the other side thereof. The ceramic wheel is mounted within a housing in accordance with the structure shown in U.S. Pat. No. 3,978,914 issued Sept. 7, 1976, to Phillips. The mounting structure includes a pair of concentric hollow shafts each carrying a wedge member at an end thereof which is biased towards the other wedge member to hold the central portion of the wheel under compression. In this way, the stresses on the ceramic wheel due to thermal expansion differences between the wheel and the mounting structure are reduced. Other types of heat exchangers may use metal wheels in place of the above-described ceramic wheel.
The heat exchanger wheel is typically provided with a gap seal arrangement which minimizes frictional drag on the wheel. A circumferential gap seal is provided about the periphery of the rotating wheel and is similar to that described in U.S. Pat. No. 4,027,721 issued June 7, 1977, to Gentry. The tapered outer surface of the ceramic wheel and an annular seal member define a small gap which provides the desired sealing structure.
In order to seal opposite sides of the heat exchanger, sealing members are provided at each face. The sealing members are typically elongate channels which extend diametrically across the wheel and spaced therefrom to define an air gap sealing relationship.
A gap seal arrangement effectively seals the edges of the wheel without creating frictional drag. Ideally, the size of the gap should be as small as possible to prevent leakage of gas between the face of the seal and the wheel since leakage may create undesirable temperature gradients. Such temperature gradients may cause thermal stresses to be formed within the wheel which could lead to cracking of the wheel.
One problem encountered with the use of gap seals is their tendency to change size as the wheel and the sealing members heat up. As the wheel heats up, expansion of the sealing material relative to the wheel causes the gap size to increase and effectively reduce the efficiency of the heat exchanger operation as well as the inducing thermal stresses. It is not possible to make these adjustments while the wheel is cold since one does not precisely know the extent of the gap seal change upon heating. Therefore, it is desirable to provide a means for adjusting the gap size during operation of the heat exchanger.